1. Field of the Invention
The present invention relates to a process for the preparation of 2,4- or 2,6-dihalogeno-aniline by reaction of an amino-benzoic acid ester with a chlorinating or brominating agent and subsequent hydrolysis and decarboxylation.
2,4- or 2,6-dichloro- and dibromo-aniline are important intermediates for the preparation of medicaments, dyes and plant protection agents.
2. Description of the Related Art
It is known to prepare 2,6-dichloroaniline in a two-step process by reaction of sulphanilamide with the equivalent amount of 30% strength hydrogen peroxide in half-concentrated hydrochloric acid at 60.degree. C. and subsequent hydrolysis of the 3,5-dichlorosulphanilamide thus obtained in 70% strength sulphuric acid at 165.degree.-195.degree. C. (Org. Synt. Coll. Vol. III (1955), 262). However, the product prepared in this way is not pure and requires purification before being used for further synthesis steps. According to DD 64,061, this process is revised by intermediate isolation of the chlorinated sulphanilamide; however, the yield of 62.5% over both process steps is unsatisfactorily low. In DD 247,670, a further process for the preparation of 2,6-dichloroaniline is described, which also starts from sulphanilamide. In this process, 2,4,6-trichloroaniline is obtained at the same time and isolated; however, the yield of pure 2,6-dichloroaniline is also low.
Another method of preparation of 2,6-dichloroaniline is described in ES 503,386, cited by C.A. 97 (1982), 162,558 t. In this case, 3,5-dichloro-4-amino-benzoic acid is reacted with potassium bromate to give 3,5-dichloro-4-bromoaniline and then reduced with zinc in alkaline solution. The preparation of pure 3,5-dichloro-4-amino-benzoic acid as the starting material is only possible, however, in poor yields (Rec. 78 (1959) 534 and Chem. Ber. 74 (1941), 807).
In JP Patent Application 57/169,447 (1982), the preparation of 2,6-dichloroaniline is described starting from 3,5-dichloro-bromobenzene, which is nitrated and hydrogenated catalytically with hydrogen to give aniline. Since the nitro group can occur in the p- and o-position to the bromine, a mixture of 2,6- and 2,4-dichloroaniline is obtained.